This is full of spoilers, so please don't read on if you haven't seen the movie.
Kenneth Lonergan wrote an incredible script. However, I'm not satisfied with his ending. This is the second fantastic movie from 2016 (the other being Hell or High Water) that went with a soft ending to the detriment of the film. This is breaking with the tradition of having a climax, and then a denouement to finish the story.
Manchester by the Sea ends with Lee, sitting at a dinner table, telling his teenage nephew Patrick that the family friend George will adopt him so that he can stay in Manchester. In the following scene, Lee and Patrick walk down a road, bouncing a ball. Lee tells Patrick that he can't stay in Manchester because he "...can't beat it," meaning he can't beat the bad memories of the place, and that he'll look for a two-bedroom apartment so that Patrick can visit him. The film closes with the two going out on the boat to fish.
The reason why this ending is so unsatisfying is because it ends with a reveal and not a completion of Lee's character arc.
A much better ending would have been: Lee drops off Patrick at George's house. They hug and hold back the tears outside of the house as Lee hands Patrick off to his new family. Let gets in his car, turns it on, and starts backing out of the driveway. He stops at the end of the driveway. He contemplates. A tear drops down his face. We see a CU of his hand fumbling around the keys near the ignition. The hand shakes. He turns off the car. Cut to Black.
This would have shown that Lee finished his arc: that he had grown to a place where he'd be willing to face all of his demons in order to honor his dead brother and take care of the nephew who he really loved.
I can't argue with Lonergan's decision. He made one of the best films of recent memory. However, I'm sick of these soft endings attached to otherwise fantastic films. This devastating film would have been so much better by alluding to greater hope for Lee's future. It would have made all the pain that we suffered while watching through the incredible sadness dissipate away in a most satisfying way.
Pop the balloon. Don't let the air squeeze out of a pinhole leak. That's no way to end a great story.